During manufacture, electronic devices are tested to assess their functionality and reliability. Such tests often include testing the electronic devices at high power levels or at high temperatures. High temperature testing accelerates failure mechanisms that cause infant mortality or early failure of the electronic devices, and allows defective electronic devices to be screened out before they are used commercially.
Conventionally, high temperature tests are carried out using a test head having a temperature controlled surface that is thermally engaged with a top surface of a device under test (“DUT”) that is installed in a test fixture—the DUT is installed in the test fixture so that its top surface is aligned to the test head. The test head is intended to maintain the DUT at a predetermined temperature during testing. However, in a manufacturing facility, after being installed in the test fixture, the top surface of the DUT may be misaligned with respect to the test head. Hence, the temperature controlled surface of the test head may not fully engage with the top surface of the DUT. As a result, thermal transfer between the test head and the DUT may not be optimum, leading to inefficient and improper testing.
To deal with such misalignment in certain testing systems, an assembly is provided that includes cylindrical flexible members for connecting a support structure and the test head. The flexible members, such as spring mountings, gimbaled mountings, and bellows mountings, enable the test head to compensate for misalignment and bring the test head in better contact with the DUT. However, the use of such flexible members adds complexity and expense to test heads, and may entail exerting excessive mechanical forces on test heads.
In testing high power electronic devices, in addition to heating, it is often necessary to cool the devices by thermal transfer to a cooling fluid flowing through the test head. Commonly used cooling fluids include water, glycol-water mixtures, fluorinated hydrocarbons, and various gases. Conventionally, the cooling fluid is supplied under pressure to the test head to force the fluid through the test head at a rate sufficient to cool the DUT. The cooling fluid is often conveyed to and from the test head using a conventional flexible fluid coupler such as a flexible tube or a flexible bellows—the flexible fluid coupler enables the test head to move so that it can be urged into contact with the top surface of the DUT.
However, the pressure of the cooling fluid within the conventional flexible fluid coupler produces unbalanced forces on the test head. For example, in a conventional flexible tube, flexible fluid coupler, fluid pressure in the tube causes it to straighten or bend, thereby putting an uncontrolled force on the test head. In a conventional flexible bellows, flexible fluid coupler, fluid pressure in the bellows causes it to expand and buckle in modes that can produce unwanted forces on the test head, thereby disturbing thermal contact of the test head to the DUT. As is well known, distortion of a flexible fluid coupler and unbalanced forces that the coupler transmits to the test head depend upon the exact shape of the flexible fluid coupler, the fluid pressure, and the flow rate of cooling fluid. Thus, uncontrolled and undesirable forces applied to a test head by conventional flexible fluid couplers is a problem that is increasing in importance in cooling high power electronic devices without causing excessive mechanical forces on the test head.
In light of the above, there is a need in the art for apparatus that solves one or more of the above-identified problems.